1 /* $OpenBSD: ungetc.c,v 1.9 2005/08/08 08:05:36 espie Exp $ */
2 /*-
3 * Copyright (c) 1990, 1993
4 * The Regents of the University of California. All rights reserved.
5 *
6 * This code is derived from software contributed to Berkeley by
7 * Chris Torek.
8 *
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
11 * are met:
12 * 1. Redistributions of source code must retain the above copyright
13 * notice, this list of conditions and the following disclaimer.
14 * 2. Redistributions in binary form must reproduce the above copyright
15 * notice, this list of conditions and the following disclaimer in the
16 * documentation and/or other materials provided with the distribution.
17 * 3. Neither the name of the University nor the names of its contributors
18 * may be used to endorse or promote products derived from this software
19 * without specific prior written permission.
20 *
21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31 * SUCH DAMAGE.
32 */
33
34 #include <stdio.h>
35 #include <stdlib.h>
36 #include <string.h>
37 #include "local.h"
38
39 static int __submore(FILE *);
40 /*
41 * Expand the ungetc buffer `in place'. That is, adjust fp->_p when
42 * the buffer moves, so that it points the same distance from the end,
43 * and move the bytes in the buffer around as necessary so that they
44 * are all at the end (stack-style).
45 */
46 static int
__submore(FILE * fp)47 __submore(FILE *fp)
48 {
49 int i;
50 unsigned char *p;
51
52 if (_UB(fp)._base == fp->_ubuf) {
53 /*
54 * Get a new buffer (rather than expanding the old one).
55 */
56 if ((p = malloc((size_t)BUFSIZ)) == NULL)
57 return (EOF);
58 _UB(fp)._base = p;
59 _UB(fp)._size = BUFSIZ;
60 p += BUFSIZ - sizeof(fp->_ubuf);
61 for (i = sizeof(fp->_ubuf); --i >= 0;)
62 p[i] = fp->_ubuf[i];
63 fp->_p = p;
64 return (0);
65 }
66 i = _UB(fp)._size;
67 p = realloc(_UB(fp)._base, i << 1);
68 if (p == NULL)
69 return (EOF);
70 /* no overlap (hence can use memcpy) because we doubled the size */
71 (void)memcpy((void *)(p + i), (void *)p, (size_t)i);
72 fp->_p = p + i;
73 _UB(fp)._base = p;
74 _UB(fp)._size = i << 1;
75 return (0);
76 }
77
78 int
ungetc(int c,FILE * fp)79 ungetc(int c, FILE *fp)
80 {
81 if (c == EOF)
82 return (EOF);
83 if (!__sdidinit)
84 __sinit();
85 _SET_ORIENTATION(fp, -1);
86 if ((fp->_flags & __SRD) == 0) {
87 /*
88 * Not already reading: no good unless reading-and-writing.
89 * Otherwise, flush any current write stuff.
90 */
91 if ((fp->_flags & __SRW) == 0)
92 return (EOF);
93 if (fp->_flags & __SWR) {
94 if (__sflush(fp))
95 return (EOF);
96 fp->_flags &= ~__SWR;
97 fp->_w = 0;
98 fp->_lbfsize = 0;
99 }
100 fp->_flags |= __SRD;
101 }
102 c = (unsigned char)c;
103
104 /*
105 * If we are in the middle of ungetc'ing, just continue.
106 * This may require expanding the current ungetc buffer.
107 */
108 if (HASUB(fp)) {
109 if (fp->_r >= _UB(fp)._size && __submore(fp))
110 return (EOF);
111 *--fp->_p = c;
112 fp->_r++;
113 return (c);
114 }
115 fp->_flags &= ~__SEOF;
116
117 /*
118 * If we can handle this by simply backing up, do so,
119 * but never replace the original character.
120 * (This makes sscanf() work when scanning `const' data.)
121 */
122 if (fp->_bf._base != NULL && fp->_p > fp->_bf._base &&
123 fp->_p[-1] == c) {
124 fp->_p--;
125 fp->_r++;
126 return (c);
127 }
128
129 /*
130 * Create an ungetc buffer.
131 * Initially, we will use the `reserve' buffer.
132 */
133 fp->_ur = fp->_r;
134 fp->_up = fp->_p;
135 _UB(fp)._base = fp->_ubuf;
136 _UB(fp)._size = sizeof(fp->_ubuf);
137 fp->_ubuf[sizeof(fp->_ubuf) - 1] = c;
138 fp->_p = &fp->_ubuf[sizeof(fp->_ubuf) - 1];
139 fp->_r = 1;
140 return (c);
141 }
142